The structures of complexes of yeast enolase and rabbit muscle pyruvate kinase have been solved to high resolution by X-ray crystallography. These structures reveal the identities of active-site residues in these two enzymes. Site-directed mutagenesis has been performed to clarify the roles of the active-site residues in catalysis. Residues believed to function as the acid/base catalysts for these enzymes are lysine 345 for yeast enolase and either arginine 72 or threonine 327 for pyruvate kinase. Both enzymes catalyze alternate reactions. NMR characterization of the products of these alternate reactions will be carried to help corroborate our hypotheses. NMR identification of the stereospecificity of reactions catalyzed by these enzymes and mutants will also be employed.